Valves are commonly used in process control systems to manipulate a flow of fluid. In general, fluid flow through a valve is controlled by adjusting the position of a control element or member (e.g., a plug) with respect to a valve seat. For example, a valve (e.g., a sliding stem valve) may include an actuator coupled to the control member via a valve stem so that force is transmitted from the actuator to change the position of the control member.
A fluid valve bonnet typically includes a mounting surface for the actuator and an opening through which the valve stem moves. A bonnet assembly may further include a packing assembly to prevent leakage around the valve stem and a seal to prevent leakage between the bonnet and the valve body.
It is often desirable to be able to remove and reinstall the bonnet so that valve components can be repaired or replaced without having to remove the valve from its connection to adjacent pipes. As such, bonnets are frequently connected to valve bodies using bolted or threaded connections, which allow the bonnet to be removed and subsequently reattached. This connection may further provide a force to pre-load the bonnet/valve body seal to optimize sealing characteristics.